Vibration damping blade



Feb. 18, 1958 ca. K. FLOROFF VIBRATION DAMPING BLADE Filed April 16, 1952 //VV/V70/? 05 R61? K. FLOROFF ATTO/Q/VE United States Patent VIBRATION DAMPING BLADE George K. Floro'if, Hawthorne, N. J., assignor to United Aircraft Corporation, EastHartford,'C0nn., a corporationof Delaware Application April 16, 1952, Serial No. 282,647

8 Claims. (Cl. 253--77) The present invention relates to vibration damped blades and other vibrating members and the method of manufacture thereof.

During operation in an elastic fluid turbine or compressor, the blades are subjected to centrifugal, thermal and aerodynamic forces and, to enable said blades to withstand heavy loads, it is necessary to dampen the vibrations .set up in .the blade. This blade vibration .dampinghas been accomplished by several devices as-by imeansofabutting shrouds located at the tip of each blade or series of blades, by reeving wires through holes or slots in the airfoil section of the blades, then securing the wires so .that they are .taut,-or by placing loose clips and the like on .the blades to combat vibration. In other instances blades have been made of several parts placed in frictional engagement with one another. Such arrangements increase the complexity of the blade and of the turbine or compressor rotor assembly and increases the manufacturing cost.

One object of the present invention is to overcome ithese objections to prior blades and methods of manutfacture thereof and to provide a one piece, vibration 'da'mped blade which is simple in construction and inexpensiveto manufacture.

Another robject of the present invention is to provide a one piece, vibration damped blade having no weight adding attachments to perform the vibration damping function;

A further object of 'the present invention is to provide a simple and inexpensive method by which one piece, vibration damped blades can be manufactured with a high degree of accuracy.

One object of the present invention is to provide a vibration damped blade of one piece construction Which can be removed or replaced without having to disturb any other part of the rotor assembly.

Other features and advantages of the invention will more fully appear from the following detailed description taken in connection with the accompanying drawings in which:

Fig. l is a perspective view of a turbine blade incorporating the invention.

Fig. 2 is a top view of such a blade.

Fig. 3 is a perspective view of a solid blade forging blank from which a blade similar to Fig. 1 may be formed.

Fig. 4 is a perspective view of a blade forging blank with one of the manufacturing steps performed.

Fig. 5 is a perspective view of the blade blank after additional manufacturing steps have been performed.

The blade 11 which, as shown, is a turbine blade, conisists of a blade tip 12, a blade root 13 and an operative portion 14 therebetween. The operative portion is airfoil in section as clearly shown in Fig. 2.

Fig. 1 shows a one piece blade which is so constructed that a slit 15 is provided at the blade tip 12 and extends almost the entire blade chord dimension. The slit extends longitudinally from the blade tip for the greater portion of the operative portion of the blade. The slit may decrease in chord dimension adjacent the lower end thereof to blend into the solid metal in the vicinity of .the blade root 13. Slit 15 is approximately centered and assumes substantially the curvature of the concave and convex surfaces of the airfoil section of the blade. Slit l5 terminates laterally within the blade 11, its edges being spaced from the leading and trailing edges of the blade as shown. Slit 15 is so positioned that it is substantially equidistant from the concave and convex surfaces of blade 11 and can be made so that it extends substantially the full chord dimension of blade 11 but is completely contained chordwise within the blade. Blade 11 is so constructed that the .opposite inner walls 20 and 22 of blade 11 which form slit 15 are in frictional engagement and, consequently, when vibrations occur in the blade, the friction caused by the rubbing of the opposite walls of slit 15 serves to damp the vibration.

It will be noted that the vibration damping slit in the blade can be placed so as to damp vibrations occurring in any portion of the blade span or chord.

One method of manufacturing the blade shown in Fig. .l is shown in Figs. 3, 4 and 5. Referring to these figures, a solid blade blank ofthe type shown in Fig. 3 isformed in which a section 16 is formed from which the blade root will bemachined anda blade section 17 of substantially cylindrical shape extends from the root portion. A column of metal is removed from the section 17 for a portion of the length of the blank as shown in Fig. 4 to produce a hole 18, the depth being substantially .the same as the depth of the slit in thecompleted blade. The section 17 of the blank is then worked, as by a forging process into the desired airfoil shape with the opposite inner walls 20 and 22 which form slit 15 in frictional engagement. Bladeinner surfaces 20 and 22 havecom- .mon forward and after edges 24 and 26. It may be necessary to apply flux .or powder to the opposite faces of slit 15 so that they will not weld together during the forging operation. It is necessary that the blank section 17 and hole 18 be of such dimension that during .the forging operation, the opposite walls of slit 15 will'be in frictional engagement when the section 17 of the blade blank has reached the desired airfoil shape. Further, it is necessary that the volume of metal remaining in blank section 17 after hole 18 is formed be substantially the same as the volume of metal needed to form a blade of desired size and shape.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other Ways without departure from its spirit as defined by the following claims.

What I claim is: i

1. A one piece blade for a turbine or compressor, said blade having inner surfaces forming a slit, said inner surfaces extending from the blade tip for a substantial portion of the blade length and further extending substantially the full chord dimension of said blade for a substantial portion of the blade length and said inner surfaces being contained within said blade, the said inner surfaces being in frictional engagement substantially throughout their entire area to provide friction damping of blade vibrations during operation.

2. The method of forming a blade which comprises forming a blank having a portion which will serve as a blade root and a second portion which will serve as the airfoil section of a blade, said second portion being substantially cylindrical in shape, then forming a hole in said blank by removing a column of metal of such size that the volume of metal remaining in the formed portion of the blank is substantially the same as the volume of metal needed to form a blade of desired size, then working said blank to reduce it to the desired airfoil shape thereby reducing the blank hole to have inner surfaces forming a slit with the inner surfaces in frictional contact substantially throughout their entire area.

3. The method of forming a blade which comprises forming a blank having a portion which will serve as a blade root and a second portion which will serve as the airfoil section of a blade, said second portion being substantially cylindrical in shape, then forming a hole in said blank by removing a column of metal from said blank which column extends substantially the full length of said second portion and being of such size that the volume of metal remaining in the formed portion of the blank is substantially the same as the volume of metal needed to form a blade of desired size, then working said blank to'reduce it to the desired airfoil shape thereby reducing the formed hole to have inner surfaces forming a slit with the inner surfaces in frictional engagement substantially throughout their entire area.

4. The method of forming a blade which comprises forming a blank having a portion which will serve as a blade root and a second portion which will serve as the airfoil section of a blade, said second portion being substantially cylindrical in shape, then forming a hole in said blank by removing a column of metal of such size that the volume of metal remaining in the formed portion of the blank is substantially the same as the volume of metal needed to form a blade of desired size, then applying a thin layer of powder to the walls of said hole to prevent metal welding during working and then working said blank to reduce it to the desired airfoil shape thereby reducing the blank hole to have inner surfaces forming a slit with the inner surfaces in frictional contact substantially throughout their entire area.

'5. The method of forming a blade which comprises forming a blank having a portion which will serve as a blade root and a second portion which will serve as the airfoil section of a blade, said second portion being substantially cylindrical in shape, thenmachining the blade root, then forming a substantially centrally located hole in said blank by removing a column of metal from i said blank which column extends substantially the full length of said second portion and being of such size that the volume of metal remaining in the formed portion of the blank is substantially the same as the volume of metal needed to form a blade of desired size, then applying a thin layer of powder to the walls of said hole to prevent metal welding during working and then work- Cir ing said blank to reduce it to the desired airfoil shape thereby reducing the blank hole to have inner surfaces forming a slit with the opposite walls in frictional contact substantially throughout their entire area.

6. A one piece blade having leading and trailing edges and having inner surfaces which form a slit which inner surfaces are substantially parallel to the opposite exterior surfaces of the blade and extend for a substantial portion of the length of the blade with the inner surfaces in contact to provide friction damping of blade vibrations, the forward and after edges of the slit being spaced from the leading and trailing edges of, the blade, said inner surfaces being in contact substantially throughout their entire area.

7. A one piece blade having inner surfaces forming a slit which inner surfaces are substantially parallel to the opposite exterior surfaces of the blade and extending from the blade tip for a substantial portion of the blade length with said inner surfaces in contact to provide friction damping of blade vibrations, the forward and after edges of the slit terminating within the blade, said inner surfaces being in contact substantially throughout their entire area.

8. A one piece blade for a turbine or compressor having an airfoil section comprising concave and convex surfaces, said blade having inner surfaces forming a slit, said inner surfaces extending for a substantial portion of the-length of the blade, the inner surfaces of said slit being in frictional engagement to provide friction damping of blade vibrations during operation and all portions of said inner surfaces being positioned substantially equidistant from the concave and convex surfaces of said blade, said inner surfaces being in contact substantially throughout their entire area.

References Cited in the file of this patent UNITED STATES PATENTS Ray Feb. 25, 1930 

